ABSTRACT Cigarillos are popular among youth and young adults, and flavors predominate in this tobacco product type. Despite carrying the same level of health risk, flavored tobacco products are misperceived by youth as being less harmful than unflavored products. A gap in the current literature exists for characterizing flavors in cigarillos and their impact on product appeal, attention to marketing, product perceptions, abuse liability, and subsequent use behavior among youth and young adults. It has yet to be determined whether the removal of flavors from cigarillos would results in cessation or substitution of another tobacco product, such as e-cigarettes, and whether that choice would be more influenced by perceptions of appeal or perceptions of risk. To accomplish this, we have proposed three integrated aims to gather data to inform CTP regulation strategies on flavored tobacco, specifically for cigarillo products; throughout the proposed research, data on JUUL will be gathered as a highly popular alternative product with potential substitutability. First, drawing from an existing Young Cigarillo User Sample, we will evaluate perceptions of flavors on appeal, risk perceptions, and addictiveness of cigarillos and other tobacco products among youth and young adult cigarillo users. Within the same sample, we will experimentally examine differences in visual attention and risk perceptions of flavored and unflavored cigarillo and JUUL advertisements among youth and young adult cigarillo users; non-users will be added to explore whether effects are modified by user type. Next, we will use a complex Experimental Tobacco Marketplace to evaluate the abuse liability/addictive potential of flavored versus unflavored cigarillos while simultaneously evaluating substitutability of JUUL e-cigarettes. Through these three aims, this proposal employs rigorous biobehavioral and behavioral economic methods to gather data that will create a foundation to inform intervention-focused research. Now that cigarillos are subject to FDA regulatory authority, these findings will be responsive to the ANPRM on the role of flavors in youth and young adult cigarillo use, and will inform policy development regarding product standards and advertising to reduce both appeal and abuse liability and to accurately inform consumers regarding cigarillo risks to health.